A wide variety of medical devices have been developed for delivery of stimulation therapy to a patient. An implantable pulse generator (IPG) system generally refers to such a medical device that delivers pulses of therapeutic stimulation. IPG systems include an IPG device and one or more implantable medical leads coupled to the IPG device. The IPG device comprises a housing that houses circuitry for the generation of the therapeutic stimulation pulses, and the leads position electrodes within the patient at locations desirable for delivery of such pulses. The IPG device is typically a biocompatible hermetically sealed structure that, like the leads, is implanted in the patient. However, in some cases, only the leads are implanted, and the IPG device resides at a location external to the patient.
One common example of an IPG device is a pacemaker. A pacemaker system typically includes a pacemaker device and one or more pacing and sensing leads for delivery of pacing pulses to a patient's heart. Another example of an IPG device is a combination pacemaker-cardioverter-defibrillator. Other examples include implantable brain stimulators, implantable gastric system stimulators, implantable nerve stimulators or muscle stimulators, implantable lower colon stimulators, and so on.
Rate control of the delivery of stimulation pulses is of paramount concern in pacemaker systems and other IPG systems. For example, stimulation of a patient's ventricles typically should not exceed 200 paces per minute. Conventionally, stimulation of the ventricles at rates above 200 paces per minute is considered very dangerous, and is sometimes considered potentially lethal. For this reason, pacemaker systems typically implement some type of rate control algorithm that limits the rate at which ventricular pacing pulses can be delivered. For example, the pacemaker may limit the ability to deliver another ventricular pacing pulse within a 300 millisecond time interval following the delivery of an earlier ventricular pacing pulse. In this manner, the pacemaker can ensure that stimulation of a patient's ventricles will never exceed 200 paces per minute.